Synoptic top level error handling

During IBEX training, one of the attendees got their synoptic into a corrupted state. When attempting to edit the synoptic, nothing would happen. We should add top level error handling so that the GUI produces an error message in such a scenario rather than just ignoring the performed action with no feedback.

Start by reproducing the corrupted synoptic state and the ignored edit action in the GUI. Trace the top-level action path and define done as displaying a useful error message instead of silently doing nothing; add or run the relevant GUI test if one is identified.

Scritto dal modello di indicizzazione a partire dal testo della issue.